Datasheet

17
®
VSP3100
OFFSET AND GAIN CALIBRATION SEQUENCE
When the VSP3100 is powered on, it will be initialized as a
3-Channel CCD, 1V internal reference mode (2V full-scale)
with an analog gain of 1, and normal output mode. This
mode is commonly used for CCD scanner applications. The
calibration procedure is done at the very beginning of the
scan.
To calibrate the VSP3100, use the following procedure:
1. Set the VSP3100 to the proper mode.
2. Set Offset to 0mV (control code: 00
H
), and PGA gain to
1 (control code: 200
H
).
3. Scan dark line.
4. Calculate the pixel offsets according to the A/D Converter
output.
5. Readjust input Offset Registers.
6. Scan white line.
7. Calculate gain. It will be the A/D Converter full-scale
divided by the A/D Converter output when the white line
is scanned.
8. Set the Gain Register. If the A/D Converter output is not
close to full-scale, go back to item 3. Otherwise, the
calibration is done.
The calibration procedure is started at the very beginning of
the scan. Once calibration is done, registers on the VSP3100
will keep this information (offset and gain for each channel)
during the operation.
RECOMMENDATION FOR POWER SUPPLY AND
GROUNDING
Proper grounding, bypassing, short lead length, and the use
of ground planes are particularly important for high-fre-
quency designs. Multi-layer PC boards are recommended
for the best performance since they offer distinct advantages
such as minimization of ground impedance, separation of
signal layers by ground layers, etc.
It is recommended that analog and digital ground pins of the
VSP3100 be joined together at the IC and connected only to
the analog ground of the system. The VSP3100 has several
analog supply pins (V
CC
), so the VSP3100 should be treated
as an analog component, and all supply pins should be
powered by the analog supply on your system. This will
ensure the most consistent results since digital supply lines
often carry high levels of noise that would otherwise be
coupled into the converter and degrade the achievable per-
formance.
As the result of the high operation speed, the converter also
generates high-frequency current transients and noise that
are fed back into the supply and reference lines. This
requires that the supply and reference pins be sufficiently
decoupled with ceramic capacitors.
Not Recommended for New Designs